Why do people call a decrease of 40% to 20% a decrease of 20% instead of 50%?

[voodoopenguin]

For the same reason when the temperature rises from 5C to 10C some people say the temperature has doubled.

Paul

[N-OS X-tasy!]

voodoopenguin wrote:
For the same reason when the temperature rises from 5C to 10C some people say the temperature has doubled.

Paul

Because the maths!

[freeradical]

rz wrote:
I argued a similar point at a sporting goods store once. Their clearance prices were 50% off. They came over the loudspeaker and said that for the next half hour, all clearance items were 75% off. So I bought something. When the clerk rang it up, she took 50% off. Then she took 25% off of that total. I explained three times that she was wrong.

If you take 75% off of $100, it's $25
If you take 50% off of $100, it's $50. If you then take 25% off of that, it's $37.50

She finally had to get a manager to ring it up properly.

In her defense, the way she rang it up is how multiple discounts are applied.

[N-OS X-tasy!]

rz wrote:
I argued a similar point at a sporting goods store once. Their clearance prices were 50% off. They came over the loudspeaker and said that for the next half hour, all clearance items were 75% off. So I bought something. When the clerk rang it up, she took 50% off. Then she took 25% off of that total. I explained three times that she was wrong.

If you take 75% off of $100, it's $25
If you take 50% off of $100, it's $50. If you then take 25% off of that, it's $37.50

She finally had to get a manager to ring it up properly.

The way this was stated ("clearance items 75% off") was straightforward and correct.

OTOH, if the offer had been stated as "an additional 25% off," the uncertainty comes from not specifying whether the additional discount is off of the starting price or the effective price after the first discount has been applied.

[Dennis S]

I had the opposite experience rz had at Dillard's. Some $100 shoes were 50/25 off and they insisted they were $25. I argued but they (the clerk and his boss) insisted. Then they showed me another pair in my size and asked if I wanted them, too. I said "sure."

[space-time]

voodoopenguin wrote:
For the same reason when the temperature rises from 5C to 10C some people say the temperature has doubled.

Paul

if you want to have some fun, use 0C and 10C (or any other value) and see how the math works out.

I had someone at work say that 80C was 33% more than 60C. Then I pointed out that if we talk about temperature change when that thing was operational, we should subtract room temperature (usually 20C) so suddenly the 80C item was only 60C above room temperature and 60C object was only 40C above room temperature, so the temperature change was now 50% more in one sample than the other. definitely not 33%.

[freeradical]

Many people do not understand that 0C is not a natural zero. It is actually an arbitrary number. So temperatures measured on either the C or F scales are interval, not ratio data.

[N-OS X-tasy!]

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[anonymouse1]

Are you buying or selling?